Final answer:
A laser backstop is a device with corner reflectors used to measure laser beams by reflecting them back to their source. This technology enables precise distance measurements, such as the increasing distance to the moon.
Step-by-step explanation:
A laser backstop is a device that is designed to detect and measure laser beams. Such a device typically includes corner reflectors, which are special mirrors that reflect light back to its source regardless of the angle at which they are hit. This technology is critical for precise measurements, such as those made by scientists to determine the distance to the moon.
Lasers emit coherent and monochromatic light, where 'coherent' refers to the photons being in-phase, and 'monochromatic' indicates that the photons have a single frequency.
By having electrons in a laser medium elevate to higher energy levels and then fall back to a lower (metastable) state, the process for emitting coherent light is initiated. The moon has corner reflectors placed on it by astronauts to allow Earth-based lasers to measure the increasing lunar distance accurately.